Liquid friction clutch

ABSTRACT

A liquid friction clutch ( 1 ) having a housing ( 2, 3 ), a clutch disc ( 4 ) rotatable relative to the housing ( 2, 3 ) and which is rotatably arranged on an end ( 5 ) of a shaft ( 6 ) which is mounted centrally within the housing ( 2, 3 ), which shaft ( 6 ) bears on its other end ( 8 ) a driveable active element ( 7 ). A working chamber ( 9 ) is positioned between the housing ( 2, 3 ) and the clutch disk ( 4 ). A storage chamber ( 10 ) is provided for the clutch fluid. A supply duct ( 11 ) leads from the storage chamber ( 10 ) to the working chamber ( 9 ). A stationary clutch part ( 13 ) relative to which the housing ( 2, 3 ) is rotatable, wherein a rotatably mounted pump element ( 14 ) is provided which, with the housing ( 2, 3 ), defines a shear gap ( 12 ).

The invention relates to a liquid friction clutch according to the preamble of claim 1.

A liquid friction clutch of said type is known from EP 1 731 787 B1, the content of disclosure of which is hereby incorporated by explicit reference in the content of disclosure of the present application.

DE 197 49 342 A1 discloses a viscous clutch for driving motor vehicle air-conditioning compressors, in which, to control the filling level of fluid in a working chamber, the throughput of fluid through the pipe section adjoining an inlet section of a scoop pipe is controlled by means of a valve. Tests carried out within the context of the invention have however yielded that such a valve causes problems in that it is extremely difficult to achieve acceptable performance results.

It is therefore an object of the present invention to provide a liquid friction clutch of the type specified in the preamble of claim 1 by means of which it is possible in a simple manner, without using a valve, to obtain a variable clutch fluid flow.

Said object is achieved by means of the features of claim 1.

By means of the provision of a rotatably mounted pump element which, with the housing, defines a shear gap, it is made possible in a simple manner, by utilizing a rotational speed difference between the pump element and the housing or the primary side of the liquid friction clutch, to generate a variable volume flow from the storage chamber into the working chamber, without it being necessary for this purpose to additionally integrate a controllable valve into the flow path.

The particular advantages of the liquid friction clutch according to the invention include firstly that only a small quantity of clutch fluid is required, because on account of the above-explained arrangement, an active feed pump is formed in the oil reservoir, which with regard to the clutch fluid quantity is advantageous over the known utilization of centrifugal forces for filling the working chamber.

Furthermore, the response behavior of the liquid friction clutch according to the invention is faster on account of the smaller clutch fluid component.

An extremely compact design is also generated because the outer diameter of the storage chamber or of the reservoir can be made larger than the inner diameter of the working chamber.

The compact design is improved further in that, as already explained above, a variability of the clutch fluid flow is made possible without the use of a valve arrangement.

The pump element which builds up a pressure, with a volume flow being generated as a result of friction of the clutch fluid in the shear gap which is preferably kept small, can be mounted either on the stationary clutch part or clutch housing of the active element (for example pump wheel, impeller, direct-current compressor etc.) or it is also possible for said pump element to be mounted on the shaft of the liquid friction clutch.

The pressure which is built up, or the volume flow which is generated, is a function of the relative rotational speed of the rotatable pump element in relation to the housing, with it being possible for the relative rotational speed to be controlled for example by means of a compensation of the drag torque of the fluid friction pump in relation to the torque that is generated by an actuating mechanism or by a brake device which may for example be designed as an eddy-current brake. Said brake device may in principle be designed as any type of magnetic brake device or friction brake. In addition to the abovementioned eddy-current brake, further examples are electric motors, generators or else viscous brakes.

If an eddy-current brake is provided as a brake device, said eddy-current brake is actuated by means of a magnetic field which is generated in a solenoid or electromagnet which compensates the magnetic field of permanent magnets provided as a further part of the brake device. A brake device of said type may be used as a fail-safe facility such that the variable feed pump or the pump element rotates at maximum throughflow rate (minimum rotational speed), specifically in a situation in which no electrical energy is applied to the solenoid.

Further details, advantages and features of the present invention will emerge from the following description of exemplary embodiments on the basis of the drawing, in which:

FIG. 1A shows a schematically highly simplified diagrammatic illustration of a liquid friction clutch according to the invention,

FIG. 1B shows a schematically highly simplified illustration of the detail X in FIG. 1A,

FIG. 2 shows a sectional illustration through one possible realization variant of the liquid friction clutch according to the invention illustrated as a diagrammatic illustration in FIG. 1,

FIG. 3 shows a detail illustration from FIG. 2 for explaining the clutch fluid flow,

FIG. 4 shows an enlarged detail illustration from FIG. 2 for explaining the magnetic flux in the liquid friction clutch according to the invention if an eddy-current brake is provided as a brake device, and

FIG. 5 shows a schematically slightly simplified perspective illustration of the liquid friction clutch according to FIG. 2.

FIG. 1A shows a highly simplified schematic illustration of a liquid friction clutch 1 according to the invention which has a housing which is constructed in the conventional way from a housing body 2 and a cover 3.

Arranged in the housing 2, 3 is a clutch disk 4 which is rotatable relative to the housing 2, 3. Here, the clutch disk 4 is rotationally fixedly arranged on an end 5 of a shaft 6 which is mounted centrally within the housing 2, 3. Fixed to the other end 8 of the shaft is a drivable active element 7 which is illustrated in schematically simplified form and which may be designed for example as a pump wheel or as an impeller.

A working chamber 9 is arranged between the housing 2, 3 and the clutch disk 4, which working chamber 9, as can be seen from FIG. 2, has working gaps 15 which make a transmission of torque possible on account of a shear action on the clutch fluid supplied to the working chamber 9.

Furthermore, a storage chamber 10 for said clutch fluid is provided, with a supply duct 11 (see FIGS. 2 and 3) leading from the storage chamber 10 to the working chamber 9.

As can be seen in particular from FIG. 2, a return pump system or a return feed pump 16 is also provided which serves for returning the clutch fluid from the working chamber 9 to the storage chamber 10.

A drive element 21, such as for example a belt pulley, is also connected to the housing 2, 3. The liquid friction clutch 1 also has a stationary clutch part 13 on which the housing 2, 3 is mounted via a main bearing 22. The stationary clutch part 13 is mounted on the shaft 6 via secondary bearings 18 and 19.

As is also shown by a juxtaposition of FIGS. 1 to 3, the liquid friction clutch 1 according to the invention is characterized by the provision of a pump element 14 which, in the example, is rotatably mounted on the shaft 6 by means of a pump element bearing 17. An alternative mounting of the pump element 14, for example on the stationary part 13, is however likewise possible.

In the illustrated example, the pump element 14 has at its radial outer edge a shear gap 12 which, according to the detail illustration in FIG. 1B, is sealed off with respect to the housing body 2 by means of sealing gaps 30 and 31. By means of this arrangement, a variable feed pump is formed which, as already explained in the introduction, permits a volume flow of clutch fluid from the storage chamber 10 to the working chamber 9 on account of a rotational speed difference to be generated between the pump element 14 and the housing 2, 3. Here, it should be emphasized that the arrangement shown on an enlarged scale in FIG. 1B is not restricted to a radial alignment of the shear gap 12. Furthermore, an axial configuration of the shear gap 12 together with corresponding sealing gaps relative to the axially adjacent housing part 32 would also be conceivable.

With regard to the volume flow explained above, reference should be made in particular to the detail illustration of FIG. 3, in which the volume flow from the storage chamber 10 into the working chamber 9 is shown by the arrows P_(A1) to P_(A4). The other arrows shown indicate the returned volume flow from the working chamber 9 into the storage chamber 10. The volume flow from the storage chamber 10 into the working chamber 9 is generated by the above-explained pump element 14 in conjunction with the explained shear gap 12. Here, the pump element 14 and the shear gap 12 form a variable feed pump, the operating principle of which is based on the rotational speed difference explained in the introduction.

To generate said rotational speed difference, it is possible to design the pump element 14 such that it can be braked. For this purpose, in FIGS. 1A, 2 and 4, an eddy-current brake is provided as a brake device, wherein any other type of suitable brake device in the form of a magnetic brake device or a friction brake is however also conceivable.

The illustrated eddy-current brake has firstly an electromagnet or solenoid 23 which is mounted at the position shown in FIG. 2. Furthermore, the brake device has permanent magnets 28 which are arranged adjacent to an eddy-current brake ring 27 (composed for example of copper) as can be seen in detail from the illustration of FIGS. 1A and 2 and from the enlarged illustration of FIG. 4. Here, in FIG. 4, the braking torque T_(B) that can be generated by the brake device is symbolized by the dashed oval circle, while the dashed oval circle T_(D) symbolizes the torque that can be generated by the pump element 14. The rotational speed of the pump element 14 is symbolized in FIG. 4 by the point S_(FP).

For further explanation, in particular of these latter components, reference may also be made to FIG. 5.

In addition to the written disclosure of the invention, reference is hereby explicitly made to the diagrammatic illustration thereof in FIGS. 1A, 1B and 2 to 5.

LIST OF REFERENCE SYMBOLS

1 Liquid friction clutch

2, 3 Housing (2: housing body, 3: cover)

4 Clutch disk

5 End of the shaft 6

6 Shaft

7 Active element (for example pump wheel, impeller etc.)

8 Second end of the shaft 6

9 Working chamber

10 Storage chamber

11 Supply duct

12 Shear gap

13 Stationary clutch part (pump housing)

14 Pump element

15 Working gap

16 Return feed pump

17 Pump element bearing

18, 19 Secondary bearings

20 Brake device

21 Drive element, in particular belt pulley on housing 2, 3

22 Main bearing

23 Solenoid/electromagnet

24 Shear gap

25 Return duct

26 Magnetic flux path

27 Ring of the eddy current brake

28 Permanent magnets

29 Gap between clutch disk 4 and housing 2, 3

30, 31 Sealing gaps

S_(FP) Rotational speed of the pump element 14

T_(B) Torque of the brake device

T_(D) Torque that can be generated by the pump element 14 

1. A liquid friction clutch (1) having a housing (2, 3), having a clutch disk (4) Which is rotatable relative to the housing (2, 3) and Which is rotatably arranged on an end (5) of a shaft (6) which is mounted centrally within the housing (2, 3) which shaft (6) bears on its other end (8) a driveable active element (7); having a working chamber (9) between the housing (2, 3) and the clutch disk (4); having a storage chamber (10) for clutch fluid; having a supply duct (11) which leads from the storage chamber (10) to the working chamber (9); and having a stationary clutch part (13) relative to which the housing (2, 3) is rotatable, characterized by a rotatably mounted pump element (14) which, with the housing (2, 3), defines a shear gap (12).
 2. The liquid friction clutch as claimed in claim 1, wherein the pump element (14) can be braked.
 3. The liquid friction clutch as claimed in claim 2, characterized by a brake device for braking the pump element (14).
 4. The liquid friction clutch as claimed in claim 3, wherein the brake device is designed as a magnetic brake device or friction brake device.
 5. The liquid friction clutch as claimed in claim 1, wherein the shear gap (12) is delimited with respect to the housing (2, 3) by sealing gaps (30, 31). 